What is PCOS (PMOS), really?

Women's health

4 July

Most people have heard of polycystic ovary syndrome (PCOS), but many are left with more questions than answers after they're diagnosed. Some women are told they have PCOS because their periods have become irregular, others first seek help because of acne, excess hair growth, difficulty falling pregnant, or trouble losing weight. Some are diagnosed after an ultrasound, while others have normal-looking ovaries despite meeting the criteria for PCOS.

Part of the confusion comes from the fact that PCOS doesn't look the same in everyone. It's better thought of as a syndrome rather than a single disease. A syndrome is simply a collection of signs and symptoms that tend to occur together, but not everyone experiences the same combination. Although it's named after the ovaries, PCOS isn't just an ovarian condition. It involves several different systems in the body, including hormones, metabolism and the way the brain communicates with the ovaries. That's one reason it can affect much more than the menstrual cycle.

Why has PCOS been renamed?

For many years, clinicians and researchers have recognised that the name polycystic ovary syndrome (PCOS) doesn't accurately describe the condition. The term suggests that ovarian cysts are the defining feature. In reality, many women diagnosed with PCOS don't have ovarian cysts at all, while others who do have polycystic-appearing ovaries don't have the syndrome. More importantly, the name focuses attention on the ovaries, when we now understand that this is a condition involving much more than reproductive health.

In 2026, after more than a decade of international collaboration involving researchers, clinicians and people living with the condition, a new name was officially adopted: Polyendocrine Metabolic Ovarian Syndrome (PMOS). The change reflects what we've learned about the condition over the past few decades and aims to better describe what is actually happening in the body. The new name highlights three important ideas:

Polyendocrine acknowledges that several hormone systems are involved, rather than a problem isolated to the ovaries.

Metabolic recognises that insulin resistance and other metabolic changes are common features of the condition and can influence both symptoms and long-term health.

Ovarian remains part of the name because the ovaries are still affected, particularly through disrupted ovulation, but they are no longer presented as the whole story.

Understanding why the name changed also helps explain why PCOS can look so different from one person to the next. Rather than being a condition that affects one organ, it involves communication between several hormonal and metabolic systems throughout the body. You'll still see the term PCOS used for some time. The transition to the new name will happen gradually over the next few years as clinical guidelines, educational resources and healthcare systems are updated.

What is actually happening in the ovaries?

To understand what happens in PCOS/PMOS, it helps to know a little about what normally occurs during the menstrual cycle. At the beginning of each cycle, several small follicles begin developing within the ovaries. Each follicle contains an immature egg. Although many follicles start growing, one usually becomes dominant. As it matures, the egg inside develops until it is released during ovulation. The remaining follicles stop developing and are gradually reabsorbed by the body. In many women with PCOS, this process doesn't progress in the usual way. Instead of one follicle becoming dominant and releasing an egg, development often stalls partway through the cycle. Ovulation may occur infrequently or not at all, and many of the small follicles remain within the ovary rather than continuing to mature.

Over time, these immature follicles can accumulate around the edge of the ovary, creating the characteristic appearance seen on ultrasound. This is often described as a "string of pearls" because the follicles appear as a ring of small, evenly spaced fluid-filled structures. Despite how they're sometimes described, these aren't ovarian cysts in the way most people think of cysts. They're simply follicles that haven't completed their normal development.

This helps explain why irregular or absent ovulation is such a central feature of PCOS. The follicles are present, but the usual process of selecting one to mature and release an egg isn't occurring consistently. It's also worth remembering that not everyone with PCOS has this appearance on ultrasound. Likewise, many women have polycystic-appearing ovaries without having PCOS.

PCOS is more than a reproductive condition

Although PCOS is often thought of as a condition that affects the menstrual cycle and fertility, its effects extend well beyond the ovaries. The same hormonal and metabolic changes that influence ovulation can also affect the skin, hair follicles, the way the body responds to insulin, and longer-term metabolic health. This is why two women with PCOS may have very different experiences, even though they're living with the same condition.

For some, irregular or absent periods are the main concern. Others are more affected by acne, increased facial or body hair, thinning scalp hair, difficulty managing weight, or challenges with fertility. Some women have very few symptoms and are only diagnosed after blood tests or an ultrasound performed for another reason.

PCOS is also associated with an increased risk of insulin resistance, prediabetes and type 2 diabetes. Depending on the individual, it may also influence cholesterol levels, blood pressure, sleep, and cardiovascular health over time. These aren't inevitable consequences, but they're part of the reason why PCOS is now recognised as a condition that deserves attention beyond reproductive health alone.

Understanding PCOS as a whole-body condition helps make sense of why treatment often involves more than simply regulating the menstrual cycle. Depending on a person's symptoms and priorities, care may also focus on supporting metabolic health, reducing long-term risk factors, or improving quality of life.

Hormones work as a team

One of the most helpful ways to think about PCOS is to stop thinking about hormones as separate chemicals acting independently. Instead, imagine them as part of an ongoing conversation. Throughout the menstrual cycle, the brain, ovaries and other organs are constantly exchanging signals. Each hormone influences the next, creating a carefully coordinated sequence of events that leads to ovulation and menstruation.

The cycle begins in the brain. Hormones released from the hypothalamus and pituitary gland signal the ovaries to begin developing a group of follicles. As these follicles grow, they produce hormones of their own, including oestrogen, which feeds information back to the brain. This two-way communication helps determine which follicle will become dominant and when ovulation should occur.

At the same time, other hormones are also contributing to the conversation. Insulin influences how the ovaries function, while fat tissue produces hormones and inflammatory signals that can affect the body's hormonal environment. Rather than working in isolation, these systems are closely interconnected.

In PCOS, communication between these different systems becomes disrupted. The signals are still there, but they are no longer as well coordinated. Ovulation may occur less often, the ovaries may produce higher levels of androgens, and changes in metabolism can reinforce these hormonal disturbances.

Insulin often plays an important role

After we eat, insulin helps move glucose from the bloodstream into the body's cells, where it can be used for energy. When the body's cells become less responsive to insulin (a state known as insulin resistance) the pancreas compensates by producing more of it. These higher insulin levels don't just affect metabolism. They also act on the ovaries, encouraging them to produce more androgens (a group of hormones that includes testosterone). Higher levels of androgens can interfere with normal follicle development and ovulation, contributing to symptoms such as irregular periods, acne, excess hair growth and thinning scalp hair. This is one of the reasons the condition was renamed. It recognises that metabolism and reproductive health are closely connected, rather than existing as two separate systems.

Not every woman with PCOS has insulin resistance, and not everyone with insulin resistance develops PCOS. However, insulin resistance is common enough that it's considered one of the major processes contributing to the condition for many women. The good news is that insulin resistance often responds well to treatment. Depending on the individual, this may involve lifestyle measures, medications, or other approaches aimed at improving the body's sensitivity to insulin.

How is PCOS diagnosed?

There isn't a single blood test or scan that can diagnose PCOS. Instead, the diagnosis is made by looking at the overall picture. Your doctor or specialist will consider your symptoms, menstrual history, physical examination, blood tests and, in some cases, an ultrasound or anti-Müllerian hormone (AMH) blood test. They will also exclude other conditions that can cause similar symptoms before confirming the diagnosis.

In adults, the current international guidelines recommend diagnosing PCOS when two of the following three features are present:

irregular or absent ovulation, often reflected by irregular menstrual cycles
clinical or biochemical signs of higher levels of androgens, such as acne, excess hair growth, or elevated androgen levels on blood tests
polycystic ovarian morphology on ultrasound, or an elevated AMH level.

Because only two of these three features are required, not everyone with PCOS has polycystic-appearing ovaries. Likewise, having polycystic-appearing ovaries on an ultrasound doesn't necessarily mean someone has PCOS. Many women without the condition have this appearance, particularly during adolescence or early adulthood. It's simply one piece of the overall picture, not a diagnosis on its own. Looking at the whole picture, rather than any single result, is what helps avoid both over- and under-diagnosis.